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Old 11-01-2010, 08:42   #16
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Single Engine in Nacelle Rib

For rudder designs I would give a cassette system such as the Vara rudder at Soca Sailboats Home Page a close look in lieu of a kick-up system. Or maybe even Tony Smith's Gemini cat system. Kick-up rudder systems can get pretty complicated, plus they usually don't steer the boat very well at all when they are kicked up in shallow water. (LOTS of weather helm).

If I were looking to use my auxiliary engine in a strictly aux manner, rather than in a motor/sailing demand, I would seriously consider a single engine installation. This engine would be conveniently mounted in an enclosure on the cockpit deck and would belt drive a steerable out-drive leg that would be incorporated into the rear portion of the central nacelle structure. Maybe this rear nacelle might appear as on "Earthling's pod" (attached photo and/or www.earthling.co.nz/boating.htm . This saves the cost and weight of the second engine, trans, shafting, prop, etc, and opens up the rears of the hulls
for a nice master bath, or whatever.
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Old 11-01-2010, 09:05   #17
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Nacelle Rib again

Originally Posted by Bob Leask
I like your idea of putting a centerboard in a nacelle on the centerline, but I've only seen that done in smaller cats. Quite a few cats use a center nacelle to break up the convergence of the two bow waves and reduce underwing pounding but for some reason I've never seen it done in larger boats. It makes sense to me for several reasons, one big board should be more effective than two smaller ones with less drag and wetted surface. Also it would uncomplicate the hull construction by eliminating the two slots. The only possible problem I can think of is placing it in an area of interaction between the two hulls, could that disrupt the flow past the board and possibly cause oscillation? Your dual assymetric CB design sounds interesting but I'm having trouble visualising it. I'd like to see a sketch if you have on

Quote:
Originally Posted by Bob
I like your idea of putting a centerboard in a nacelle on the centerline, but I've only seen that done in smaller cats. Quite a few cats use a center nacelle to break up the convergence of the two bow waves and reduce underwing pounding but for some reason I've never seen it done in larger boats. It makes sense to me for several reasons, one big board should be more effective than two smaller ones with less drag and wetted surface. Also it would uncomplicate the hull construction by eliminating the two slots. The only possible problem I can think of is placing it in an area of interaction between the two hulls, could that disrupt the flow past the board and possibly cause oscillation? Your dual assymetric CB design sounds interesting but I'm having trouble visualising it. I'd like to see a sketch if you have one.
Don't have a lot of detail in drawings at this moment, as it is an alternate proposal I am suggesting for consideration, and that may have some resistance to overcome as does my unusual sailing rig.

NOTE: There is a requirement for a transverse bulkhead in the boat structure at this CB location to which diagonal 'wires' can be attached to offset the big side-loads of the CB's.
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